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The FBI believes it knows the identities of the thieves who stole art valued at up to $500 million from Boston's Isabella Stewart Gardner Museum in 1990 and that some of the art was taken here to Connecticut.

Richard DesLauriers, the FBI's special agent in charge in Boston, said the thieves belong to a criminal organization based in New England and the mid-Atlantic states.

The priceless works of art have yet to be found, and a publicity campaign will be launched to urge members of the public to provide tips that lead to recovering the paintings.

There's also a $5 million reward in the case involving 13 stolen works, including masterpieces by Rembrandt, Vermeer, Degas and Manet.

On one night in March 1990, two people dressed as Boston police officers went into the Boston museum, handcuffed the guards, brought them to the basement and stole 13 pieces of priceless art, including work by Rembrandt, Manet and Degas.

DesLauriers said authorities believe the art was taken to Connecticut and the Philadelphia region in the years after the theft, and offered for sale in Philadelphia about a decade ago.

The FBI held a news conference on Monday to discuss the case, but would not provide much information on who the suspects are. They did, however, say that a member of the FBI based in New Haven is among the investigators on the case.

It also has a new website aimed at getting help cracking the case at www.FBI.gov/gardner.

The agency will also be posting videos on social media sites, and raising awareness using digital billboards in the Philadelphia region.

The FBI asks stressed that anyone with information about the artwork call the FBI at 1-800-CALL-FBI (1-800-225-5324) or the museum directly or through a third party.

“In the past, people who realize they are in possession of stolen art have returned the art in a variety of ways, including through third parties, attorneys, and anonymously leaving items in churches or at police stations,” Special Agent Geoffrey Kelly, who is the lead investigator in the case and a member of the Art Crime Team, said.